In the case of operating a service for transferring data on a network, a communication device is disposed on the network. The communication device generally includes HW (hardware) such as L2SW (Layer 2 Switch), and a control CPU (Central Processing Unit) that controls the HW according to a control program. Incidentally, the communication device updates the control software, as needed, so as to improve functions or correct problems. At this time, the communication device is required to implement ISSU (In Service Software Upgrade), which is a technique for completing an updating operation for control software in-service without interrupting data transfer so as to continuously operate the service.
As a system for implementing the ISSU, a system in which information held by a control CPU is stored before a control program is updated and the information is restored after the control program is updated is generally employed. However, due to some causes, the information restored by the control CPU may be inconsistent with information held by a management server or information held by HW. This is caused because, for example, the setting for the HW is changed by the management server during a period in which the information held by the control CPU is stored and restored. In this case, it is necessary to specify the location where there is an inconsistency. However, assuming that a system administrator has to determine whether or not there is an inconsistency in the information restored by the control CPU, there is a need to temporarily stop the service every time the control software is updated. Accordingly, there is a demand for minimizing adverse effects on the continuously operated service, even when there is an inconsistency in the information restored by the control CPU.
A related art is disclosed in, for example, PTL 1. In the technique disclosed in PTL 1, a difference record indicating a difference between a record of the current generation and a record obtained one generation ago (environmental elements changed during a transfer to the current generation, and operation information obtained in the current generation) is generated and the difference record is displayed in the case of a failure or the like.